Electrophotographic materials and methods employing photoconductive resinous charge transfer complexes



United States Patent 3,408,183 ELECTROPHOTOGRAPHIC MATERIALS AND METHODS EMPLOYING PHOTO- CONDUCTIVE RESINOUS CHARGE TRANSFER COMPLEXES Joseph Mammino, Penfield, N.Y., assignor to Xerox Corporation, Rochester, N.Y., a corporation of New York No Drawing. Filed Jan. 18, 1965, Ser. No. 426,409 26 Claims. (CI. 96-15) ABSTRACT OF THE DISCLOSURE Photoconductive materials are prepared from phenolaldehyde resins and Lewis acids. The material are charge transfer complexes. The photoconductive materials are used to make electrophotographic plates, methods of using the plates are also disclosed.

This invention relates to electrophotography and more particularly to an improved photoconductive insulating material adapted for use in an electrophotographic plate.

In electrophotography, it is known to produce electrostatic images on the surface of a photoconductive insulating layer by uniformly charging the insulating layer and then dissipating this charge on that portion of the layer which is exposed to light. The latent image formed thereon will correspond to the configuration of the light image passing through the master to be reproduced. This image is rendered visible by depositing on the insulating layer a finely divided developing material comprising a colorant called a toner and a toner carrier. The powder developing material will normally be attracted to that portion of the layer retaining a charge thereby distributing itself over the layer in a manner corresponding to the electrostatic image. The powder image may then be transferred to paper or other recording surfaces. The paper, upon being separated from the insulating layer, will bear the powdered image which may subsequently be made permanent by heating or other suitable fixing means. This above general process is detailed in U.S. Patents 2,297,691; 2,357,908; 2,891,011; and 3,079,342.

It is known that various photoconductive insulating materials may be used in making electrophotographic plates. Suitable photoconductive insulating materials such as anthracene, sulfur, selenium or mixtures thereof have been disclosed by Carlson in U.S. Patent 2,297,691. These materials generally have a sensitivity in the blue or near ultraviolet range and all but selenium have a further limitation of being only slightly light sensitive. For this reason, selenium has been the most commercially accepted material for use in electrophotographic plates. Vitreous selenium, however, while desirable in most aspects, suffers from the serious limitations of, first, its spectral response is somewhat limited to the near ultraviolet blue and green region of the spectrum, and, secondly, the preparation of vitreous selenium plates requires complicated, costly and complex procedures such as vacuum evaporation.

Further, selenium plates require the use of a separate conductive substrate layer, preferably with a further barrier layer thereon before deposition of the selenium photoconductor. Because of these economic and commercial consideration, there have been many recent efforts to develop photoconductive insulating materials other than selenium for use in electrophotographic plates.

It has been proposed that various two-phase materials may be used to prepare a photoconductive insulating layer for use in the manufacture of electrophotographic plates. It is known, for example, to use inorganic photoconductive pigments dispersed in suitable binder material to form this photoconductive insulating layer. It has further 3,408,183 Patented Oct. 29, 1968 See been demonstrated that organic photoconductive insulating dyes and a wide variety of polycyclic compounds may be used together with suitable resin materials to form photoconductive insulating layers useful in binder type plates. In each of these two systems, it is required that at least one initial component used to prepare the photoconductive insulating layer be, of itself, a photo conductive insulating material. In a third type plate, inherently photoconductive insulating polymers are used frequently in combination with sensitizing dyes or Lewis acids to form the photoconductive insulating layer. Again, in this type of plate, at least one photoconductive insulating component is required in the manufacture of the layer. While the process of increasing sensitivity is by itself desirable, commercially speaking, it does have the drawback of limitation to only those materials already having substantial photoconductivity.

These three known plates are similar to those defined in U.S. Patents 3,097,095; 3,113,022; 3,041,165; 3,126,281; 3,073,861; 3,072,479; 2,999,750; Canadian Patent 644,167 and German Patent 1,068,115.

The polymeric and binder-type organic photoconductor plates of the prior art generally have the inherent disadvantages of high cost of manufacture, brittleness, and poor adhesion to supporting substrates. A number of these photoconductive insulating layers have substantially low temperature distortion roperties which make them undesirable in an automatic electro-photographic apparatus which often includes powerful lamps and thermal fusing devices and tends to heat up the Xerographic plate. Also the limitation in choice of physical properties has been dictated by the restriction to using only inherently photoconductive materials.

lnorganic pigment binder-type plates are limited in usefulness because they are often opaque in color and are thus limited in use to a system where light transmission is not required. These inorganic pigment binder plates have the further disadvantage of not being reusable due to fatigue and not readily cleaned because of their rough surfaces. Still another disadvantage of these known photoconductive insulating materials is that in their manufacture, the materials used have been restricted to those having photoconductive insulating properties. Therefore, the optical properties such as transparency, color and sensitivity range are limited to those materials of known photoconductors.

It is, therefore, an object of this invention to provide a photoconductive insulating material suitable for use in electrophotographic plates devoid of the above noted disadvantages.

Another object of this invention is to provide an economical method for the preparation of photoconductive insulating materials wherein none of the required components is by itself substantially photoconductive.

Another object of this invention is to provide a photoconductive insulating material suitable for use in electrographic plates in both single use and reusable systems.

Yet another object is to provide a photoconductive insulating layer for an electrophotographic plate which is substantially resistant to abrasion and has a relatively high distortion temperature.

Yet a further object of this invention is to provide an electrophotographic plate having a wide range of useful physical properties.

A still further object of this invention is to provide photoconductive insulating layers which may be cast into self-supporting binder-free photoconductive films and structures heretofore unobtainable.

Still another object of this invention is to provide a novel combination of initially non-photoconductive in sulating materials suitable for use in the manufacture of the photoconductive insulating layer of a xerographic plate which are easily coated on a desired substrate or combined with a conductive layer.

Another object is to provide a transparent self-supporting photoconductive film adapted for xerographic imaging without requiring a conductive backing.

A still further object of this invention is to provide a photoconductive insulating material which may be made substantially transparent and particularly adapted for use in systems where light transmission is generally required.

The foregoing objects and others are accomplished in accordance with this invention, generally speaking, by providing a photoconductive material adapted for use in electrophotographic plates which is obtained by complexing:

(A) a suitable Lewis acid with (B) a composition having a molecular weight of at least about 300,

and having repeating units Wherein:

R is a residue of a member selected from the group con sisting of formaldehyde, paraformaldehyde, furfural amino formaldehyde, acrolein, benzaldehyde, chloral, oxo-aldehydes, acetaldehyde, glyoxal, propionaldehyde, n-butyraldehyde, isobutyraldehyde, n-valeraldehyde, isovaleraldehyde, n-caproaldehyde, n-heptaldehyde, stearaldehyde, crotonaldehyde, and mixtures thereof;

Y is a member selected from the group consisting of hydrogen, OH, lower alkyl (having up to six carbon atoms), halogen and mixtures thereof;

X is a member selected from the group consisting of above R and oxygen;

Z is an integer having a. value of at least 2;

n is an integer having a value of from 1-4; and

m is an integer having a value of from l-3.

It should be noted that neither of the above two components (A and B) used to make the photoconductor of this invention is by itself photoconductive; rather, they are nonphotoconductive. After the above substantially non-photoconductive Lewis acid is mixed or otherwise complexed with said substantially nonphotoconductive resinous material, a highly desirable photoconductive insulating material is obtained which may be either cast as a self-supporting layer or may be deposited on a suitable supporting substrate. Any other suitable method of preparing a photoconductive plate using the resulting photoconductive material may be used.

It has been found by the present process that electron acceptor complexing may be used to render inherently non-photoconductive electron donor-type insulators photoconductive and thus to greatly increase the range and selection of useful materials of electrophotography.

A Lewis acid, therefore, is any electron acceptor relative to other reagents present in this system; for example, a Lewis acid will tend to accept a pair of electrons furnished by an electron donor (or Lewis base) in the process of forming a chemical compound or, in the present invention, a charge transfer complex.

A Lewis acid is defined for the purposes of this invention as any electron accepting material relative to the polymer with which it is complexed.

A charge transfer complex may be defined as a molecular complex between substantially neutral electrondonor and acceptor molecules, characterized by the fact that photo-excitation produces internal electron transfer to yield a temporary excited state in which the donor is more positive and the acceptor more negative than in the ground state.

It is believed that the donor-type insulating resins of the present invention are rendered photoconductive by the formation of charge transfer complexes with electron acceptors, or Lewis acids, and that these complexes, once formed, constitute the photoconductive elements of the plates.

Broadly speaking, charge transfer complexes are loose associations between electron donors and acceptors, frequently in stoichiometric ratios which are characterized as follows:

(a) Donor-acceptor interaction is weak in the neutral ground state, i.e. neither donor nor acceptor are appreciably perturbed by each other in the absence of photo-excitation.

(b) Donor-acceptor interaction is relatively strong in the photo-excited state, i.e. the components are at least partially ionized by photo-excitation.

(c) When the complex is formed, one or more new absorption bands appear in the near ultraviolet or visible region (wave lengths between 3200-7500 A.U.) which are present in neither donor alone nor acceptor alone, but which are instead a property of the donor/ acceptor complex.

It is found that both the intrinsic absorption bands of the donor and the charge transfer bands of the complex may be used to excite photoconductivity.

Photoconductive insulator for the purposes of this invention is defined with reference to the practical application to xerographic imaging. It is generally considered that any insulator may be rendered photoconductive by excitation and or radiation of sufliciently short Wave lengths of adequate intensity. This statement applies generally to inorganic as well as to organic materials, including the inert binder resins used in binder plates, the electron acceptor type activators presently used, and the aromatic resins used in the present invention. However, the short wave length radiation sensitivity is not useful in practical imaging systems because adequately intense sources of wave lengths below 3200' angstrom units are not available, because such radiation is damaging to the human eyes, and because this radiation is absorbed by glass optical systems. Accordingly, we define the use of the term photoconductive insulators to those which are characterized as follows:

(1) They may be formed into continuous films which are capable of retaining electrostatic charge in the absence of actinic radiation.

(2) These films are sufiiciently sensitive to illumination of wave lengths longer than 3200 AU. to be discharged by at least one-half by a total flux of at most 10 quanta per centimeter of absorbed radiation.

This definition excludes the resins and Lewis acids of our disclosure, when these are used separately, from the class of photoconductive insulators.

The resins used in the present invention may be gen erally defined as phenol-aldehyde type resins. Any suitable phenolaldehyde resin may be used depending on the immediate needs and required properties. Typical phenols useful in making phenol-aldehyde resins are: phenol, cresol, xylenol, alkyl phenols, such as p-tertiary amyl phenol, p-cyclohexyl phenol; aryl phenols such as p-phenyl phenol, triphenylp-hydroxy phenol; alkenyl phenols such as para, and ortho-l,5, di and 1,3 di-butenyl phenol, 1,3,5, tri-butenyl phenol; halogenated phenols such as mono, di, tri and tetra chlorinated phenol, resorcinol, hydroquinone, and mixtures thereof; sulfonated phenols such as p-hydroxy-ter-butyl-benzene sulfonic acid, dihydric, trihydric and polyhydric phenols such as resorcinol, catechol, hydroquinone, pyrocatechol, pyrogallol, phloroglucinol,

benzenetriol, xylenol, polynuclear phenols such as alpha and beta naphthol, anthracene phenol; dihydroxy-diphenyl alkanes such as Bisphenol A and mixtures thereof. Any suitable substituted phenol as above noted may also be used to prepare the phenolic type resin useful in this invention. Modified phenol-aldehyde resins may also be used if desired; for example, the phenol-formaldehyde type resins may be modified with diphenyl-oxide to form a phenol-formaldehyde type resin having an oxygen bridge between at least one aromatic group.

A typical modified phenol-formaldehyde resin of this kind is a diphenyl-oxide modified Novolak resin identified as ET 395 and manufactured by the Dow Chemical Company. This modified Novolak is the product resulting from the reaction of dimethyl-diphenyloxide with phenol under conditions which allow for the formation of a novolak structure. Typical properties for this material are:

Softening pointfi C. 75-100 Color Straw to amber. Chlorine, percent 0.1.

Hydroxyl, percent 69.

Molecular weight MOO-12,000.

Ring and ball method.

The softening point and molecular weight may be controlled by the ratio of phenol to dimethyl-diphenyl oxide reaction mixture.

In general, the highly reactive phenols form condensation products that cure rapidly to hard insoluble resins, while phenols of low reactivity form condensation products that show little or no tendency to harden. The major structural feature of a phenol that determines its reactivity with aldehydes is its functionality. This may be defined as the total number of unsubstituted positions on the benzene ring that are in ortho and para position to the hydroxyl group. An ortho-para directing group in the meta position enhances the reactivity of the phenol.

Any suitable aldehyde may be used in the reaction with the phenol. Typical aldehydes are: formaldehyde, paraformaldehyde, furfural, amino formaldehyde, acrolein, benzaldehyde, chloral, oxo-aldehydes, acetaldehyde, glyoxal, propionaldehyde, n-butyralde hyde, isobutyraldehyde, n valeraldehyde, isovaleraldehyde, n caproaldehyde, n-heptaldehyde, stearaldehyde, crotonaldehyde, and mixtures thereof.

Any suitable Lewis acid can be complexed with the above noted phenol-aldehyde type resins to form the desired photoconductive material. While the mechanism of the complex chemical inter-reaction involved in the present process is not completely understood, it is believed that a charge transfer complex is formed having absorption bands characteristic of neither of the two components considered separately. The additon to and mixture with one non-photoconductive component and the other seems to have a synergistic effect, that is much greater than additive.

Best results are obtained when using these preferred Lewis acids: 2,4,7-trinitro-9-fiuorenone, 4,4-bis (dimethylamino) benzophenone, tetrachlorophthalic anhydride, chloranil, picric acid, benz(a)anthracene-7,12-dione and 1,3 ,5 -trinitrob enzene.

Other typical Lewis acids are quinones, such as -benzoquinone,

2 ,5 -dichlorobenzoquinone, 2,6-dichlorobenzo quinone, chloranil, naphthoquinone- 1,4) 2,3-dichloronaphthoquinone-( 1,4) anthraquinone, 2-methy1anthraquinone, 1,4-dimethylanthraquinone, l-chloro anthraquinone, anthraquinone-Z-carboxylic acid, 1,5 -dichloroanthraquinone, 1-chloro-4-nitroanthraquinone, phenanthrene-quinone, acenaphthenequinone, pyranthrenequinone, chrysene-quinone,

6 thio-naphthene-quinone, anthraquinone-1,8-disulfonic acid and anthraquinone-Z- aldehyde; triphthaloylbenzene; aldehydes such as bromal, 4-nitrobenzaldehyde, 2,6-dichlorobenzaldehyde, 2-ethoxy-1-naphthaldehyde, anthracene-9-aldehyde, pyrene-3-aldehyde, oxindole-3-aldehyde, pyridine-2, 6-dialdehyde, biphenyl-4-aldehyde; organic phosphonic acids such as 4-chloro-3-nitrobenzene-phosphonic acid, nitrophenols, such as 4-nitrophenol, and picric acid; acid anhydrides, for example; acetic anhydride, succinic anhydride, maleic anhydride, phthalic anhydride, tetrachlorophthalic anhydride, perylene-3, 4,9,10-tetracarboxylic acid and chrysene-2,3,8,9-

tetracarboxylic anhydride, di-bromo maleic acid anhydride;

metal halides of the metals and metalloids of the groups IB, II through to group VIII of the periodical system, for example: aluminum chloride, zinc chloride, ferric chloride, tin tetrachloride, (stannic chloride), arsenic trichloride, stannous chloride, antimony pentachloride, magnesium chloride, magnesium bromide, calcium bromide, calcium iodide, strontium bromide, chromic bromide, manganous chloride, cobaltous chloride, cobaltic chloride, cupric bromide, ceric chloride, thorium chloride, arsenic triiodide; boron halide compounds, forexample: boron trifluoride, and boron trichloride; and ketones, such as acetophenone, benzophenone, 2-acetyl-napthalene, benzil, benzoin, S-benzoyl-acenaphthene, biacenedione, 9- acetyl-anthracene, 9-benZoyl-anthracene, 4-(4 dimethylamino-cinnamoyl)-1-acetylbenzene, acetoacetic acidanilide, indandione-(1,3), (1,3-diketo-hydrindene), acenaphthenequinonc-dichloride, anisil, 2,2-pyridil and furil.

Additional Lewis acids are mineral acids such as the hydrogen halides, sulphuric acid and phosphoric acid; organic carboxylic acids, such as acetic acid and the substitution products thereof, monochloro-acetic acid, dichloroacetic acid, trichloro-acetic acid, phenylacetic acid, and 6-methyl-coumarinylacetic acid(4); maleic acid, cinnamic acid, benzoic acid,

1-(4-diethyl-amino-benzoyl)-benzene-2-carboxylic acid, phthalic acid, and

tetra-chlorophthalic acid, alpha-beta-dibromo-beta-formyl-acrylic acid (mucobromic acid)-dibromo-maleic acid, 2-bromo-benzoic acid,

gallic acid,

3-nitro-2-hydroxyl-l-benzoic acid, 2-nitro'phenoxy-acetic acid, Z-nitro-benzoic acid,

3-nitro-benzoic acid,

4-nitro-benzoic acid, 3-nitro-4-ethoxy-benzoic acid, 2-chloro-4-nitro-l-benzoic acid, 2-chloro-4-nitro-l-benzoic acid, 3-nitro-4-methoxy-benzoic acid, 4-nitro-1-methyl'benzoic acid, 2-chloro-5-nitro-l-benzoic acid, 3-chloro-6-nitro-l-benzoic acid, 4-chloro-3-nitro-l-benzoic acid, 5-chloro-3-nitro-2-hydroxy-benzoic acid,

4-chloro-2-hydroxy-benzoic acid,

2,4-dinitro-l-benzoic acid,

2-bromo-5-nitro-benzoic acid,

4-chlorophenyl-acetic acid,

2-chloro-cinnamic acid,

Z-cyanocinnamic acid,

2,4-dichlorobenzoic acid,

3,5-dinitro-benzoic acid,

3,5-dinitro-salicylic acid,

malonic acid, mucic acid, acetosalicylic acid, benzilic acid, butane-tetracarboxylic acid, citric acid, cyano-acetic acid, cyclo-hexane-dicarboxylic acid, cyclo-hexene-carboxylic acid, 9,10-dichloro-stearic acid, fumaric acid, ita

conic acid, levulinic acid, (levulic acid), malic acid, succinic acid, alpha-bromo-stearic acid, citraconic acid,

dibromo-succinic acid,

pyrene-2,3,7,8-tetra-carboxylic acid,

tartaric acid;

organic sulphonic acids,

such as 4-toluene sulphonic acid, and

benzene sulphonic acid 2,4-dinitro-l-methylbenzene-6- s-ulphonic acid,

2,6-dinitro-l-h3xdroxy-benzene-4-sulphonic acid,

2-nitro-1-hydroxy-benzene-4-sulphonic acid,

4-nitro-l-hydroxy-2-benzene sulphonic acid,

3-nitro-2-methyl-l-hydroxy-benzene-5-sulphonic acid,

6-nitro-4-methyl-l-hydroxy-benzene-2-sulphonic acid,

4-c'nloro-1-hydroxy-benzene-3-sulphonic acid,

Z-chioz-c-3 nitro-1-methyl-benzene-S-sulphonic acid and 2-chlcrol -rnethyl-benzene-4-sulphonic acid.

The following examples will further define the specifics of the present invention. Parts and percentages are by weight unless otherwise indicated. The examples below should be considered to illustrate various preferred embodiments of the present invention.

Test procedure for determining photoconductivity as indicated in T ables I and 11 noted after the examples The substance to be evaluated is coated by suitable means onto a conductive substrate and dried. The coated plate is connected to ground and the layer is electrically charged in the dark by a corona discharge device (positive or negative) to saturation potential using a needle point scorotron powered by a high voltage power supply manufactured by Hivolt Power Supply Co., Condenser Division, Model PS-lO-l M operating at 7 1w. while maintaining the grid potential at 0.9 kv. using a Kepco, Inc. regulated DC supply (-1500 v.) Charging time is 15 seconds.

The potential due to the charge is then measured with a transparent electrometer probe without touching the layer or affecting the charge. The signal generated in the probe by the charged layer is amplified and fed into a Moseley Autograf recorder Model 680. The graph directly plotted by the recorder describes the magnitude of the charge on the layer and rate of decay of the charge with time. After a periodof about 15 seconds, the layer is illuminated by shining light onto the layer through the transparent probe using an American Optical Spence Microscope Illuminator containing a GE. 1493 medical type incandescent lamp operating at 2800 K. color temperature. The illumination level is measured with a Weston Illumination Meter Model #756 and is recorded in the tables. The light discharge rate is measured for a period of 15 seconds or until a steady residual potential is reached.

The numerical difference in the rate of discharge of the charge on the layer with time in the light minus the rate of discharge of the charge on the layer in the dark is tion to alight and shadow image and developing the latent charge image by cascade using a commercial developer, depending on the polarity of the initial corona charge given to the photoconductive material. Details of this procedure are cited in Example I.

EXAMPLE I About a five gram sample of a diphenyloxide modified Novolak resin No. ET-395-1300 (manufactured by the Dow Chemical Company) and discussed above, is put into a ml. beaker containing about 45 grams of a solvent mixture consisting of about 25 grams acetone and about 20 grams toluene. The mixture is agitated by means of a stirrer until the resin is fully dissolved in the solvent.

About two hundred and fifty mg. of 2,4,7-trinitrofiuorenone are added to about a 10 gram portion of the diphenyloxide modified Novolak resin solution prepared as above (contained in a two ounce jar.) The mixture is stirred as before until solution of the 2,4,7-trinitrofluorenone is achieved.

The above solution is applied onto an aluminum plate (0.005 x 11" x 16 flat rectangular sheet of bright finished 1145-H19 aluminum foil made by the Aluminum Company of America) by suitable means such as a wire wound bar, dip coated, flow coated, whirler coated, etc. and the aluminum plate is dried. The solution is applied onto the plate until the thickness of the dried layer amounts to about 5 microns.

A 5 /2" x 5 /2" portion of the above plate is negatively charged to about 300 volts by means of a corona discharge, exposed for about 15 seconds by projection using a Simmon Omega D3 enlarger equipped with an f4.5 lens (at a color temperature of 2950 K.) The illumination level at the exposure plane is four foot-candles as measured with a Weston Illumination Meter Model #756. The plate is then developed by cascading Xerox 1824 developer over the plate. The image developed on the plate corresponds to the projected image. The developed image is then electrostatically transferred to a receiving sheet and fused. The plate is then cleaned of residual toner and is reused as by the above described process.

A different 5%." x 5 /2" portion of the above plate is charged, exposed-and developed as previously described. The image developed on the plate is fused directly thereon.

Another 5 /2" x 5 /2" portion of the plate is electrometered as previously described and the results are tabulated. See Table I.

Another 5 /2 x 5 /2" portion of the above plate is negatively charged to about 300 volts by a corona discharge device, exposed for 45 seconds using a tungsten light source (color temperature 2950 K., illumination level incident upon the filter. is 2.8 foot-candles,) exposed by contact to a spectral interference wedge filter (Jeana Glaswerk Schott, Mainz; Nr. 8-234559) and developed by cascading a commercial developer (such as is described in United States Patent 3,079,342) over the plate. The image developed on the plate is fused. Inspection of the image developed on the plate shows that the photoconductive layer is sensitive to light of about 380 to 600 millimicrons.

EXAMPLE II The above procedure of Example I is repeated using Amberol F 71, a rosin modified phenol-formaldehyde resin type available from the Rohm and Haas Company. The results are tabulated.

EXAMPLE III The above procedure of Example I is repeated using Amberol ST-137X available from the Rohm and Haas Company, a non-reactive unmodified 100% phenolformaldehyde resin. The results are tabulated.

Each of the resinsdescribed above is mixed with 2,4,7- trinitrofluorenone as described in Example I and tested for photoconductivity. The plates are charged negatively by corona discharge, exposed and developed with a commercial developer, (such as is described in United States Patents 2,618,551 and 3,079,342.) The image developed on each of these plates corresponds to the Original projected image. The developed image on each plate is electrostatically transferred to a receiving sheet and fused. The plate is then cleaned of residual toner and made ready for reuse. 7

Other plates prepared according to Examples II and III were also tested by the electrometer measurement procedure as outlined above. The results are tabulated in Table I.

EXAMPLE IV A coating solution is prepared as described in Example I except about 250 milligrams of benz(a)anthracene-7,12- dione is added in place of 2,4,7-trinitrfiuorenone to the diphenyloxide modified Novolak resin solution. The above prepared solution is coated onto an aluminum substrate and dried. The coated sheet is then electrometered as previously described and the data tabulated. (See Table I.)

- EXAMPLE VI A coating solution is prepared as described in Example I except about 100 mg. of aurintricarboxylic acid is added in place of 2,4,7-trinitrofiuorenone to the diphenyloxide modified Novolak resin solution. The above prepared solution is coated onto an aluminum substrate and dried. The coated sheet is then electrometered as previously described and the data tabulated. (See Table I.)

EXAMPLE. .VII

Another sample is prepared by a method similar to that of Example I except that 200 milligrams of 1,3,5- trinitrobenzene are added to the diphenyloxide Novolak resin rather than the Lewis acid of Example V. (See Table I.)

EXAMPLE VIII This sample is prepared by a method similar to that of Example I except that 200 milligrams of 2,3-dichloro- 1,4-naphthaquinone is used rather than the Lewis acid of Example I. (See Table I.)

EXAMPLE IX About a 30 gram sample of a phenolic resin (CKM 5254) manufactured by Union Carbide Plastics Company, obtained by reacting 1 mole of p-phenyl-phenol with less than 1 mole of formaldehyde, is put into a 250-ml. (Pyrex) glass beaker containing about 200 g. of a 1:1 solvent mixture of acetone and toluene. The mixture is agitated by a stirrer until the resin is fully dissolved in the solvent.

About 9 ml. of a 0.02% w/v solution of 2,4,7-trinitrofluorenone in toluene and about 10 ml. of cyclohexane is added to about a g. portion of the p-phenyl-phenol phenolic resin solution prepared as above (contained in a 100 ml. beaker). The composition is stirred-as before until all of the materials are well dispersed.

The above solution is applied onto an aluminum plate by suitable means and dried.

A portion of the above prepared plate is negatively charged to about 250 volts by means of a corona discharge, exposed for about 15 seconds using the Simmon Omega D3 enlarger as light source. The plate is developed by cascading a commercial developer (such as is described in United States Patents 2,618,551 and 3,079,342 over the plate. The image developed on the plate corresponds to the projected image. The developed image is then electrostatically transferred to a receiving sheet and fused. The plate is cleaned of residual toner and may be reused by the above described process.

Another portion of the above prepared plate is charged, exposed and developed as above. The image developed on the plate is heat fused directly thereon.

Another portion of the plate is electrometered as previously described and the results are tabulated. (See Table I.)

EXAMPLES X to XIII Coatings are prepared of each of the resin types described in Examples I, II, III and IX but without any Lewis acid additive. Electrometer measurements are made on these coatings and the data tabulated. Tests on the resins by themselves indicate that these are nonphotoconductive. (See Table I.)

EXAMPLE XIV About a 1 g. portion of Lucite 2042, an ethyl methacrylate resin, is dissolved in a solvent blend consisting of 10 ml. of methyl ethyl ketone, 1 ml. of benzene, 1 ml. of acetane and 2 ml. of diethyl ketone. The mixture is agitated by a stirrer until the resin is fully dissolved in the solvent.

The above solution is applied onto an aluminum plate by suitable means and dried.

The above plate is electrometered and the results tabulated. (See Table I.) This plate is used as a control.

EXAMPLE XV About 250 mg. of 2,4,7-trinitrofluorenone is added to a coating solution prepared as described in Example XIV above. The solution is applied to a conductive substrate as described and the plate is electrometered and the data are tabulated. (See Table I.)

EXAMPLE XVI About 250 mg. of benzophenone tetracarboxylic dianhydride is added to a coating solution prepared as described in Example XIV above. The solution is applied to a conductive substrate as described and the plate is electrometered and the data are tabulated. (See Table I.)

EXAMPLE XVII About 250 mg. of benz(a)anthracene-7,l2-dione is added to a coating solution prepared as described in Example XIV above. Thesolution is applied to a conductive substrate as described and the plate is electrometered and the data are tabulated. (See Table I.)

EXAMPLE XVIII About mg. of aurincarboxylic acid is added to a coating solution prepared as described in Example XIV above. The solution is applied to a conductive substrate as described and the plate is electrometered and the data are tabulated. (See Table I.)

EXAMPLE XIX About 250 mg. of 1,3,5-trinitrobenzene is added to a coating solution prepared as described in Example XIV above. The solution is applied to a conductive substrate as described and the plate is electrometered and the data are tabulated. (See Table 1.)

EXAMPLE XX About 250 mg. of 2,3-dichloro-1,4-naphthaquinone is added to a coating solution prepared as described in Ex- '1 1 ample XIV above. The solution is applied to a conductive substrate and the plate is electrometered and the data are tabulated. (See Table I.)

.The data in Examples XIV to XX shows that the Lewis acids tested are non-photoconductive in an inert binder resin.

EXAMPLE XXI About 1 gram sample of diphenyloxide modified Novolak resin No. ET 395-1300 (manufactured by The Dow Chemical Company) and discussed above, is put into a 100-ml. glass beaker containing grams of acetone and about 5 grams of toluene. The mixture is agitated with a stirrer until the resin is fully dissolved in the solvent blend.

About 100 mg. of 2,4,7-trinitrofiuorenone is added to the above prepared diphenyloxide modified Novolak resin solution and stirredas before until solution of the 2,4,7- trinitrofluorenone is achieved.

About mg. of Pyronin B dye is dissolved in a solvent mixture consisting of 5 ml. of cyclohexane and 5 drops of dimethyl formamide (contained in a 25 ml. Pyrex glass beaker) and added to the diphenyloxide modified Novolak resin-2,4,7-trinitrofluorenone solution prepared above. The mixture is stirred until the dye is thoroughly dispersed.

The above solution is applied onto a 5 /2" x 5 /2" fiat sheet of aluminum foil by suitable means to achieve a layer of about 5 microns and the plate is air dried for about 5 minutes and oven dried at about 70 C. for one hour.

The above prepared plate is electrometered and the results tabulated. (See Table II.)

EXAMPLE XXII A coating solution is prepared as described in Example XXI above except that 10 mg. of Methylene Green dye is added to the diphenyloxide modified Novolak resin-2,4,7- trinitrofluorenone solution in place of Pyronin B dye. The above prepared plate is electrometered and the results tabulated. (See Table II.)

12 EXAMPLE XXIII A coating solution is prepared as described in Example XXI'above except that 10 mg. of Brilliant'Green dye is added to the diphenyloxide modified Novolak resin-2,4,7- trinitrofluorenone solution in place of Pyronin B dye.

The above prepared plate is negatively charged to about 300 volts by a corona discharge device, exposed by contact for thirty seconds through the spectral wedge filter mentioned above, using a tungsten light source operating at 2950 K. color temperature. The illumination incident upon the spectral wedge filter is 2.8 foot-candles. The image is developed by cascading a commercial developer such as is described in United States Patents 2,618,551 and 3,079,342 over the plate. The image developed on the plate is fused. Inspection of the image developed on the plate shows that the photoconductive layer is sensitive to light of about 380 to 700 millimicrons.

Another plate is prepared as above and electrometered and the results are tabulated. (See Table II.)

Example A coating solution is prepared as described in Example XXI above except that 10 mg. of Eosine Y dye is added to the diphenyl-oxide modified Novolak resin-2,4,7-trinitrofluorenone solution in place of Pyronin B dye.

Another plate is prepared in the same manner. The results are tabulated. (See Table II.)

Example XXV TABLE I.-ELECIROMETER DATA ON PHOTOCONDUCTIVE PHENOLIC RESINS Initial Potential Dark Discharge Light Discharge Volts Residual Illumination Sensitivity, Example (volts) (volts/sec.) (volts/sec.) Potential Alter (it.-candles) (volts/ 15 Secs. !t.-c.-sec.)

III +170 2. 7 3. 8 120 0. 8 200 0 4. 4 130 3. 3

VI +495 trace 94 0. 0 I45 1. 3 3. 33 102 2. 2

VII +440 1. 4 10. 7 325 94 9. 9 -470 1. 7 14. 8 340 13. 9

VIII +300 2. 0 20. 0 170 94 19. 2 310 2. 7 20. 0 18. 4

IX +250 4. 1 28. 2 100 23 105. 0 -320 3. l 49. 6 100 202. 0

CONTROL EXPERIMENTS XII 1. 0 1.0 170 135 0 -310 0 0 310 0 XIII 85 1. 0 1. 0 70 99 0 90 0. 9 0.9 85 0 XIV +460 4. 4 4. 4 394 94 0 500 5. 3 5. 3 420 0 XV +550 1. 0 1. 0 535 U4 0 525 1. 0 1. 0 510 0 TABLE ICntinued Initial Potential Dark Discharge Light Discharge Volts Residual Illumination Sensitivity, Example (volts) (volts/sec.) (volts/sec.) Potential After (ft-candles) (volts/100 Secs. ft.-c.-sec.)

XVI +420 1. 7 l. 73 395 94 0 440 2. 2 2. 2 405 0 XVII +360 0. 9 0. 9 345 94 0 360 4. 7 4. 7 285 94 0 XVIII 50 0 0 50 94 0 0 0 20 0 XIX +360 0 0 360 94 0 480 2. 0 2. 0 450 0 TABLE II Initial Potential Dark Discharge Light Discharge Volts Residual Illumination Sensitivity, Example (volts) (volts/sec.) (volts/sec.) Potential After (ft-candles) (volts/100 15 Secs. it.-c.-sec.)

XXI +130 1. 0 26. 7 45 62 42 200 1. 5 57. 2 40 90 XXII +155 3. 8 24. 3 45 62 34 -230 1. 5 93. 4 40 148 XXIH +265 5. 3 186. 5 62 292 335 2. 1 48. 0 10 771 XXIV +345 6. 2 155. 5 55 62 241 420 5. 3 266. 5 45 422 XXV +120 1. 0 11- 9 50 62 18 l 0 17. 3 4O 29 In the above tables, sensitivity represents the initial discharge rate upon illumination in volts/100 ft.-c.-sec. corrected for-the rate of dark discharge. As shown by Examples I-IX, a mixture of a phenol aldehyde resin and a Lewis acid is photoconductive. Examples X-XIII show that phenol aldehyde resins are not photoconductive when used alone. Example XIV indicates that an inert binder, Lucite 2042, is not photoconductive. Examples XV-XX show that the Lewis acids as used in Examples IIX are not photoconductive in an inert binder resin. In Table II, Examples XXIXXV show that the phenol aldehyde resin and Lewis acid mixture may be sensitized by sensitizing dyes.

While a useful photoconductor will result from mixtures comprising from about 1 to about 100 parts of resin for each one part Lewis acid, for optimum sensitivity and reusability it is preferred that from about 1 to about 5 parts of resin be mixed with each one part Lewis acid.

Although specific materials and conditions were set forth in the above examples, these were merely illustrative of the present invention. Various other compositions, such as the typical materials listed above and various conditions where suitable, may be substituted for those given in the examples with similar results. The photoconductive composition of this invention may have other materials or colorants mixed therewith to enhance, sensitize, synergize or otherwise modify the photoconductive properties of the composition. The photoconductive compositions of this invention, where suitable, may be used in other imaging processes, such as those disclosed in copending applications Serial Nos. 384,737; 483,680 and 384,681, where their electrically photosensitive properties are beneficial.

Many other modifications of the present invention will occur to those skilled in the art upon a reading of this disclosure. These are intended to be encompassed within the spirit of this invention.

What is claimed is:

1. A photoconductive charge transfer complex material comprising a mixture of a phenolaldehyde resin and a Lewis acid, said photoconductive charge transfer complex material having at least one new absorption band within a range of from about 3200 to about 7500 angstrom units.

2. The photoconductive charge transfer complex material of claim I wherein said Lewis acid is selected from at least one member of the group consisting of 2,4,7-trinitro-9-fiuorenone, 4,4-bis (dimethylamino benzophenone, tetrachlorophthalic anhydride, chloranil, picric acid, ben(a) anthracene-7,12-dione, 2,3-dichloro-1,4-naphthaquinone and 1,3,5-trinitrobenzene.

3. Thephotoconductive charge transfer complex material of claim 2 wherein said Lewis acid is 2,4,7-trinitro- 9-fiuorenone.

4. The photoconductive material of claim 1 comprising from about 1 to about parts of resin for every one part of Lewis acid.

5. The photoconductive material of claim 1 wherein said resin has the following general formula:

R is a residue of a member selected from the group consisting of formaldehyde, paraformaldehyde, furfural, amino formaldehyde, acrolein, benzaldehyde, chloral, oxo-aldehydes, acetaldehyde, glyoxal, propionaldehyde, n-butyraldehyde, isobutyraldehyde, n-valeraldehyde, isovaleraldehyde, n-caproaldehyde, n-heptaldehyde, stearaldehyde, crontonaldehyde and mixtures thereof;

Y is a member selected from the group consisting of hydrogen, OH, lower alkyl, halogen and mixtures thereof;

X is a member selected from the group consisting of above R and oxygen;

Z is an integer of at least 2;

n is an integer having a value of from 1 to 4; and

m is an integer having a value of from 1 to 3.

6. The photoconductive material of claim 5 wherein said resin comprises the reaction product of a phenol and formaldehyde.

7. The photoconductive material of claim 5 wherein said resin comprises the reaction product of dimethyldiphenyloxide and phenol.

8. A process for the production of a photoconductive charge transfercomplex material which comprises mixing a phenol-aldehyde resin and a Lewis acid, said photoconductive charge transfer material having at least one new absorption band within arange of from about 3200 to about 7500 angstrom units.

9. The photoconductive charge transfer complex material ofclaim 8 wherein said Lewis acid is selected from at least one member of the group consisting of 2,4,7-trinitro-9-fiuorenone, 4,4-bis dirnethylarnino benzophenone, tetrachlorophthalic anhydride, chloranil, picric acid, ben(a) anthracene-7,l2-dione, 2,3-dichloro-1,4-naphthaquinone and 1,3,5-trinitrobenzene.

10. The photoconductive charge transfer complex material of claim-9 wherein said'Lewis acid is 2,4,7-trinitro- 9-fiuorenone.

11. The process of claim 8 wherein from about 1 to about 100 parts of resin are mixed for every one part of Lewis acid.

12. The process of claim 8 wherein said resin has the wherein:

R is a residue of a member selected from the group consisting of formaldehyde, paraformaldehyde, furfural, amino formaldehyde, acrolein, benzaldehyde, chloral, oxo-aldehydes, acetaldehydes, propionaldehydes, n butyraldehyde, isobutyraldehyde, n-valeraldehyde, isovaleraldehyde, n-caproaldehyde, n-heptaldehyde, stear aldehyde, crotonaldehyde, and mixtures thereof;

Y is a member selected from the group consisting of hydrogen, OH, lower alkyl, halogen and mixtures thereof;

X is a member selected from the group consisting of above R and oxygen;

Z is an integer having a value of at least 2;

n is an integer having a value of from 1 to 4; and

m is an integer having a value of from 1 to 3.

13. The process of claim 12 wherein said resin comprises the reaction product of a phenol and formaldehyde.

14. The process of claim 12 wherein said resin comprises the reaction product of a phenol-formaldehyde resin and diphenyl oxide.

15. An electrophotographic plate comprising a support substrate having fixed to the surface thereof a photoconductive charge transfer complex material comprising a mixture of a phenol-aldehyde resin and a Lewis acid, said photoconductive charge transfer complex material hav ing at least one new absorption band within the range of from about 3200 to about 7500 angstrom units.

16. The plate of claim 15 wherein said Lewis acid is selected from at least one member of the group consisting of 2,4,7-trinitro-9-fiu0renone, 4,4-bis(dimethylamino)benzophenone, tetrachlorophthalic anhydride, chloranil, picric acid, benz(a) anthracene-7,l2-dione, 2,3-dichloro-1,4-naphthaquinone and 1,3,5-trinitrobenzene.

17. The plate of claim 16 wherein said Lewis acid is 2,4,7-trinitro-9-fluorenone.

18. The plate of claim 15 comprising from about 1 to about 100 parts of resin for every one part of Lewis acid.

19. An electrophotographic process wherein the plate of claim 15 is electrically charged in an image pattern and developed with electrically attractable marking particles.

20. The process as disclosed in claim 19 further including the steps of transferring said marking particles to a receiving sheet and recharging and developing said plate to produce at least more than one copy of the original.

21. The electrophotographic plate of claim 9 wherein said phenol-aldehyde resin has the following general formula:

O H O H sow wherein R is a residue of a member selected from the group consisting of formaldehyde, paraformaldehyde, furfural, amino formaldehyde, acrolein, benzaldehyde, chloral, oxo-aldehydes, acetaldehyde, propionaldehyde, nbutyraldehyde, isobutyraldehyde, n-valeraldehyde, isovaleraldehyde, n-caproaldehyde, n-heptaldehyde, stearaldehyde, crotonaldehyde and mixtures thereof;

Y is a member selected from the group consisting of hydrogen, OH, lower alkyl, halogen and mixtures thereof;

X is a member selected from the group consisting of above R and oxygen;

Z is an integer having a value of at least 2;

n is an integer having a value of from 1 to 4; and

m is an integer having a value of from 1 to 3.

22. An electrophotograph-ic process wherein the plate of claim 15 is electrically charged, exposed to an image pattern to be reproduced and developed with electrically attractable marking particles.

23. The process as disclosed in claim 22 further including the steps of transferring said marking particles to a receiving sheet, and recharging, exposing and developing said plate to produce at least more than one copy of the original.

24. An electrophotographic process wherein the plate of claim 21 is electrically charged, exposed to an image pattern to be reproduced and developed with electrically attractable marking particles.

25. A method of forming a latent electrostatic charge pattern comprising uniformly charging the electrophotographic plate of claim 9 and exposing said plate to a pattern of activating electromagnetic radiation.

26. An electrophotographic process in which the plate of claim 4 is electrically charged in an image pattern and developed with electrically attractable marking particles.

References Cited UNITED STATES PATENTS 2,319,142 5/1943 Lebach 26059 2,655,490 10/ 1953 Sonnabend et al 26059 3,037,861 6/1962 Hoegl et a1 96-1 3,056,754 10/ 1962 Giller 2603 3,300,419 1/ 1967 Erickson 260-25 NORMAN G. TORCHIN, Primary Examiner. J. C. COOPER III, Assistant Examiner. 

